William, thank you for your thoughtful question.
The fact is that schism is a terrible sin, and worse than heresy. But the vast majority of people belonging to a 'separated' group are not schismatics at all. From my perspective as a priest sitting in the UK, is a devout, elderly Christian of the Romanian Orthodox Church a schismatic? I don't think so. The Romanian Orthodox Christian may not even know there is a Coptic Orthodox Church, and may not know anything truthful about my Church in any case. On what basis then is such a faithful Christian a schismatic?
Is Max Michel, the Egyptian who has set himself up in our own times as a pseudo-bishop in Egypt a schismatic? Most certainly. He is worthy of every criticism and condemnation, and those who join themselves to him, cutting themselves off from the life of the Church are in grave and present danger of being schismatics with him.
But not everyone associated with a 'separation' is a schismatic. If a man has decided to leave the Church and join Max Michel's group he is probably a schismatic if he does so with knowledge and intent. But is his 10 year old son a schismatic? I don't see how that would be a just or reasonable conclusion. And if after some years, the 10 year old son who becomes a 20 year old man just keeps going to the same 'Church' he has always known (as the vast majority of religious people do) then he is not necessarily a schismatic either.
If he became an activist for his cause, and actively propagated the separation into a new generation then he might well be worthy of being considered a schismatic. But if he is just going to 'Church' and trying to be Orthodox as he has understood it so far then he might be misled, deceived, in error, but he would not strike me as a schismatic.
The Fathers understood this, and in the anti-Chalcedonian movement it was always the case that the ordinary folk were to be treated with great leniency when they sought to be reconciled with the Church. It was understood that generally they were not participants in any sin of schism, or even wittingly in any heresy, and were received by a simple renunciation of error and confession of faith. The Fathers of the anti-Chalcedonian Orthodox movement never considered that the Chalcedonians had altogether ceased to be the Church. This is why we have not baptised or even chrismated any coming to our communion until the most recent decades. St Severus speaks of 'illegal re-anointing' as an 'abominable practice'.
Even today, where Eastern Orthodox are permitted to receive communion from our hands it is on the basis of their confessing no heresy, urging no schism, and by their desire and faithfulness in worship manifesting that Orthodoxy which has been required by the Fathers. To desire to worship with us eliminates any trace of schism. Schism is a sin of the will not a matter of jurisdiction.
It might be possible for me to consider that a member of a notionally 'hard-line' Eastern Orthodox jurisdiction might have no trace of schism in their heart, while a member of an ostensibly 'friendly' Eastern Orthodox jurisdiction might be eaten up by it. (And there are one or two of my own communion who are also apparently and as far as they can be known on the internet, eaten up by schism, even while members of the Church).
Is it serious that the Eastern Orthodox communion has separated itself from our Orthodoxy? Yes, of course. This is why there have not ceased to be efforts made to bring about reconciliation. The fact of the Islamic domination of the Middle East has made things very difficult in this regard. But that is no longer a factor, and it is now easy to communicate, where there is a will. Now we must see whether both sides indeed do have a will to be reconciled. Schism is not manifest simply by the fact of being separated. This is part of history. It is manifest as a sin in the hearts of those who perpetuate division.
There were dialogues all through the 6th and into the 7th centuries. There was a short lived reunion in the 7th century. There was the possibility of reunion in the 19th century. There is certainly a human division within the Church, and to say this is impossible is manifestly and historically false. But it is for us to see whether we add to division through our own cultivation of the sin of schism, or whether we do all that is possible and reasonable and appropriate to heal the wounds of the past.
I was born into and brought up in the Plymouth Brethren, a group whose distinctive beliefs I almost entirely reject as plain wrong. But was I separated from God and steeped in schism and heresy just by being born into such a situation? Or was I already on the spiritual pilgrimage to where I am now? I believe the latter, both of myself and of most people. We cannot help where we are born, we cannot easily choose what we know or learn, but we can choose what we do with what we know and learn. Had I discovered Orthodoxy, properly and with consideration, and rejected it, then I might well be guilty of separating myself in schism and heresy. But my whole life has been a journey towards and into Orthodoxy.
I take the same view towards Eastern Orthodox. All of us are on a spiritual journey. Is this one or that one growing in Orthodoxy, in love and truth, or is this one or that one turning in on themselves, fearfully narrowing and hardening their heart in schism? Where we start is not so much the issue. Just as the Fathers teach that we are born mortal but not sinful, so I would suggest that we are born into situations of broken-ness and division but not born schismatic. We choose to become sinners and schismatics ourselves.